1. Field of the Invention
The present process is directed to the separation of alkenes, e.g., butene from polyunsaturated hydrocarbons such as alkadienes, e.g., butadiene by preferentially hydrocyanating alkadienes in mixture with alkenes to their corresponding nitriles and thereafter recovering the unreacted alkenes.
2. Description of the Prior Art
The hydrocyanation process employed in the separation process of the present invention is well defined. In commercial application it includes a two-step reaction, e.g., the sequential addition of hydrogen cyanide to a diolefin such as butadiene to first produce 3- and/or 4-pentenenitrile and then to produce adiponitrile as the second step. The present invention employs a reaction similar to this first step in the hydrocyanation process. A full description of this first step is contained in U.S. Pat. No. 3,496,215 issued on Feb. 17, 1970 and includes a description of the general type of catalyst which is employed and the temperatures and pressures at which the hydrocyanation should be conducted. Additional discussion of the first step of the hydrocyanation reaction using a .pi.-allyl nickel complex catalyst is found in U.S. Pat. No. 3,850,973 issued on Nov. 26, 1974.
A process of hydrocyanating terminal alkynes is disclosed in U.S. Pat. No. 3,496,210 issued on Feb. 17, 1970. The disclosures of the foregoing references are incorporated herein by this reference.
U.S. Pat. No. 3,496,215 suggests that the addition of HCN to a double bond can be accomplished with both diolefins and monoolefins (Column 1, lines 45-60). Applicant has discovered that under the conditions herein disclosed hydrogen cyanide can be preferentially reacted with a diolefin contained in a mixture comprising monoolefins which have physical properties close to the diolefin and thereby producing an unsaturated nitrile from the diolefin from which the monoolefin can be readily separated, e.g., by distillation.